1. Field of the Invention
This invention relates to a thermal printer.
2. Description of the Related Art
A thermal printer is disclosed in, for example JP-A-60-38181, wherein a rigid and cylindrical capstan roller (transport roller) is used for transporting a printing paper. A head and wear-resistive material such as tungsten carbide is firmly coated on the surface of this transport roller by using, for example, a plasma jet. The printing paper is supplied from a supply roll (printing paper roll) having the printing paper wound therearound in the form of a roll, and a tension is always imparted to the printing paper being transported between the printing paper roll and a platen roller. In a standby mode, the printing paper passed between a thermal head and the platen roller is maintained in its stationary state with its leading end firmly held between the transport roller and a pinch roller (pressure applying roller). Generally, the thermal head has a flat surface in a vicinity of its heat generator part including an array of heat generator elements, and the printing paper pressed onto the thermal head in a print mode has inevitably a curvature at the heat generator part of the thermal head. In other words, the path of transporting the printing paper cannot generally be made straight in the vicinity of the heat generator part of the thermal head. For this reason too, the platen roller having a cylindrical shape is used in the prior art thermal printer as the part which is disposed opposite to the heat generator part of the thermal head so as to press the printing paper onto the heat generator part of the thermal head. The above fact indicates that a restraining force tending to cause curling of the printing paper by the curvature of the platen roller acts on the printing paper when the thermal printer is maintained in the standby mode.